Collagenase has been localized in human corneas using immunocytochemical techniques employing a specific antiserum to human skin collagenase. The enzyme was found in vivo in ulcerating corneas, whereas in corneas obtained from a variety of nonulcerative conditions, no immunologic evidence of the enzyme was seen. Corneal collagenase was present only in the stromal portion of the cornea, suggesting that cells from this tissue are the source of the enzyme. The localization of collagenase to the corneal stroma was reproduced by placing either ulcerating or nonulcerating corneas in tissue culture, indicating that the organ culture system may represent a model that duplicates some conditions present in corneal disease.